The following relates to the nuclear reactor fuel assembly packaging and transportation arts, to shipping containers for unirradiated nuclear fuel assemblies, to apparatus for manipulating such shipping containers, to shipping and handling methods utilizing same, and to related arts.
Unirradiated nuclear fuel assemblies for light water nuclear reactors typically comprise 235U enriched fuel pellets, and in a typical configuration comprise an array of parallel fuel rods each comprising a hollow cladding inside of which are disposed 235U enriched fuel pellets. The 235U enrichment of the fuel pellets is typically less than 5% for commercial nuclear power reactor fuel.
Transportation of unirradiated nuclear fuel assemblies is accomplished using shipping containers that meet appropriate nuclear regulatory rules, e.g. Nuclear Regulatory Commission (NRC) rules in the United States. Under NRC rules, the shipping containers are designed to preclude the release of radioactive material to the environment and to prevent nuclear criticality from occurring in the event of postulated accidents. Furthermore, the shipping containers are designed to protect the unirradiated fuel from damage during shipment.
Existing nuclear fuel shipping containers are typically “clamshell” designs that are rectangular or cylindrical in shape and consist of a lower shell, one or more internal “strongbacks” that support the fuel assemblies, and a removable top shell that encloses the fuel assemblies. A flanged joint between the top and bottom shells allow the container to be opened and closed by bolted or pinned connections along the periphery of the container. A fuel assembly is generally loaded into the shipping container by removing the top shell from the container and lifting the empty lower shell to a vertical position. The fuel assembly is positioned vertically when not supported by a strongback. The vertical fuel assembly is lifted with a crane and then moved laterally (i.e. sideways while remaining suspended upright by the crane) into the upright lower shell of the clamshell container until it is positioned against the strongback of the container. In some designs, several clamps along the length of the fuel assembly may be incorporated to secure the fuel assembly to the strongback. Some designs utilize hinged doors that cover the fuel and are clamped in place to secure the fuel assembly. After the fuel assembly is secured, the shipping container is placed in a horizontal position and the top shell is installed. The shipping container is shipped in the horizontal position. At the nuclear reactor site, the process is reversed, i.e. the top shell is removed, the lower shell with the fuel assembly still loaded on the strongback is up-ended from the horizontal position to the vertical position, and the fuel assembly is unclamped from the strongback and lifted out using a crane and loaded into the nuclear reactor. See, e.g. Sappey, U.S. Pat. No. 5,263,064; Sappey, U.S. Pat. No. 5,263,063.
The clamps and doors used in clamshell type shipping containers have certain disadvantages. For example, the hinged connections and clamping mechanisms can generate metal shavings that can become trapped inside the fuel assemblies and lead to fretting failure of the fuel rods. The mechanical parts such as bolts, nuts, and washers, can become detached and may lead to fuel rod failure if the loose parts become trapped inside the fuel assembly. The securing mechanisms entail certain adjustments to avoid applying excessive forces on the fuel assemblies, and have the potential to become loose during transport. These securing mechanisms also adds time to the processes of loading and unloading the fuel assemblies from the containers. Moreover, the clamshell container can hold only one or two fuel assemblies, such that the complete set of loading and unloading operations may need repeated for each fuel assembly that is transported from the factory to the nuclear reactor site.
The operation of moving the shipping container (or lower shell) with loaded fuel between the horizontal and vertical positions is typically performed using a dedicated piece of equipment, which is referred to in the art as an “up-ender” (even when used to move the loaded shipping container from the vertical position to the horizontal position). Existing up-enders are typically complex dedicated pieces of equipment that have numerous components and that occupy substantial storage space when not in use. See, e.g. Ales et al., U.S. Pub. No. 2007/0241001 A1.